If it is the long stringy kind (hair algae, as opposed to the shorter beard algae which only grows a couple inches), then it can be easily removed by twirling it around an old toothbrush or filter brush, like wrapping cotton candy around a cone. It will pop it off at the attachment point and you can remove the whole strand this way, no broken pieces to grow back. I used this method diligently for about 2 weeks (daily removing all that i could see) and completly eradicated a serious infestation of the stuff from my tank.